For the German tanks I usually go for the sides and rear of that big turret. Also rear of the tank is fairly vulnerable on all of those tanks (IS-7 especially). If your gun is too small to penetrate those spots you can try hitting their tracks - if you can make them immobile they'll become a juicy target for artillery.

Alternately you can just HE-spam them, hoping to do as much module damage as you can.

EDIT: I see you have an IS-7 yourself, with quite a few battles on it - how come you didn't learn this yet?

Maus: The lower front plate between the tracks can easily be penetrated by higher tier tanks.

If you cannot penetrate them and use HE, aim for the front of the turret. In my experience you do more damage by aiming at the gun, then on the turret side/tank front/tank side. Exception: IS7 usually bounces my HE on turret, lol.

- The lower hull armor generally.
- Tanks have different stats. For example, a T30 does much more damage per shot than a IS-7 (but has a slower Rate of Fire). Also: some SPGs can oneshot tanks in some cases.